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Holy flux: spatial and temporal variation in massive pulses of emerging insect biomass from western U.S. rivers
Author(s) -
Walters David M.,
Wesner Jeff S.,
Zuellig Robert E.,
Kowalski Dan A.,
Kondratieff Matt C.
Publication year - 2018
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1002/ecy.2023
Subject(s) - variation (astronomy) , biomass (ecology) , ecology , spatial variability , flux (metallurgy) , content (measure theory) , spatial ecology , geography , temporal scales , environmental science , biology , mathematics , statistics , chemistry , physics , organic chemistry , astrophysics , mathematical analysis
The river stonefly, Pteronarcys californica (aka salmonfly), is an iconic insect in rivers of western North America due to its large size and its support of economically important species like wild trout (Nehring et al. 2011). Their emergence generates a large economic subsidy to local communities, as anglers from around the world travel to western rivers to fish the salmonfly “hatch” (e.g., Willoughby 2013). Salmonflies, which have a 4-yr lifespan in the central Rocky Mountains (Nehring et al. 2011), emerge en masse during 1 week in late spring (Sheldon 1999), and more than 20 terrestrial species, including humans, are known to eat adult salmonflies (Muttkowski 1925, Sutton 1985, Rockwell et al. 2009). How they influence populations of insectivores or the broader river-riparian ecosystem is unknown; this itself is an issue because salmonflies are disappearing from some rivers (Nehring et al. 2011). We observed massive synoptic emergence of salmonflies from some western rivers, but not others (Fig. 1), and wondered how large and temporally variable these fluxes might be, which could have implications for local riparian consumer populations. We quantified salmonfly emergence and carbon (C) flux over 5 yr from 21 river reaches within 5 major rivers in Colorado and Wyoming (Appendix S2: Tables S1–S3, Figs. S1–S4). We then compared our direct estimates of salmonfly C flux (i.e., an aquatic resource subsidy) to modeled estimates of total yearly emergent insect production using a global model based on stream size (Gratton et al. 2009). Emerging aquatic insects represent a globally important subsidy from freshwater habitats to terrestrial consumers (Baxter et al. 2005). For example, an estimated 6,800 t C yr 1 are moved from water to land in the state of Wisconsin by emerging aquatic insects (USA, Bartrons et al. 2013). While aquatic-to-terrestrial and other resource subsidies are ubiquitous, their effects have largely been measured by experimentally manipulating subsidy presence or absence, an approach that assumes that the time-averaged amount of the subsidy is the primary factor limiting consumer abundance (Hastings 2012).